The long-term goal of this study is to elucidate the cellular and molecular mechanism(s) responsible for the decline in skeletal muscle performance with age. Age-related decreases in skeletal muscle mass, strength and quality (contractile properties, fiber type composition, etc.) are termed sarcopenia and contribute to physical disability and loss of independence. The hypothesis of this proposal is that viral-mediated expression of IGF-1 in spinal cord prevents excitation-contraction uncoupling, loss in type IIB fibers and decreases in skeletal muscle force with aging. This hypothesis will be assessed using the following specific aims: 1) To determine whether viral-mediated administration of IGF-1 results in sustained expression of IGF-1 in mouse spinal cord. To this end, young (7 months), middle-aged (14), and old (28) C57BL/6 mice will be studied at different times of the adenovirus construct administration. Skeletal muscle and several other peripheral tissues will be screened for the presence of the vector and IGF-1 expression. 2) To establish whether IGF-1 expression in spinal cord prevents muscle denervation and loss of type IIB fibers in muscles from aging C57BL/6 mice. Muscle fiber denervation will be studied using a technique developed in our laboratory, to identify a newly expressed tetrodotoxin resistant Na+ channel population in denervated whole muscle and single fibers. Fiber type composition will be done using monoclonal antibodies against myosin heavy chain isoforms in rAAV-injected and non-injected young, middle-aged and old mice. 3) To determine whether sustained expression of IGF-1 in spinal cord prevents excitation-contraction-uncoupling in single intact muscle fibers from aging mice. The decline in specific force is associated with decreases in peak intracellular calcium concentration in single intact fast and slow-twitch muscle fibers. In this part of the project we will demonstrate that this process is under neural control and that expression of hIGF-1 in spinal cord neurons restores excitation-contraction coupling. 4) To establish whether neural expression of IGF-1 prevents age-related decline in DHPR and RyR1 gene expression in single muscle fibers. A combined electrophysiological and molecular biology strategy will be used to determine that the DHPR alpha1 subunit and RyR1 mRNA expression in single muscle fibers is under neural control and that gene expression of these receptors can be restored by neural expression of hIGF-1.